An increasing body of evidence suggests that the nervous system plays an important role in craniofacial development. Clinically, patients suffering from inherited lysosomal storage diseases often exhibit growth impairment, skeletal abnormalities and craniofacial malformations, as well as neurodegeneration, blindness, mental retardation, paralysis and dementia. Currently, there is no preventive or comprehensive treatment for this class of disorders. The neurons of the brain, trigeminal and spinal root ganglia display swollen vacuolated perikarya stored with excessive amounts of complex macromolecules, leading to neuronal dysfunction and impaired innervation. Based on these observations, we hypothesize that normal neuronal function is required for craniofacial development, and that neuronal dysfunction due to lysosomal storage may contribute to aberrant craniofacial development. To address this hypothesis, we will employ an animal model with severe craniofacial dysostosis, growth retardation and facial dysmorphism associated with excessive neuronal storage of mucopolysaccharides and GM2 gangliosides due to lack of beta-hexosaminidase (hexA-/-/hexB-/- double knockout mice). The expression of a transgene encoding for human beta-hexosaminidase under the control of a tightly regulated inducible expression system will be targeted to the neurons of hexA-/-/hexB-/- mice. Utilizing this murine model we will determine whether neuronal function is required for normal craniofacial development by conditionally restoring beta- hexosaminidase activity in neurons during critical developmental periods. Moreover, we will develop gene therapy strategies for the treatment of beta-hexosaminidase deficiency, employing the Herpes Simplex Virus-1 (HSV) Amplicon and the Feline Immunodeficiency Virus (FIV) systems. We will administer the beta-hexosaminidase therapeutic gene centrally (brain) as well as peripherally (affected craniofacial structures), and compare their treatment efficacy in vivo. Although this mouse model does not replicate a human disease per se, it provides the opportunity to (1) investigate the role of neuronal function in aberrant craniofacial development seen in lysosomal storage diseases, (2) evaluate the use of neurotropic viruses for the delivery of therapeutic genes, and (3) assess the efficacy of perinatal gene therapy in the treatment of inherited metabolic disorders.